This invention relates to methods for adjusting the fuel injection quantity of an internal combustion engine for regulating smoothness of operation, especially for automobiles.
In automobiles, low frequency vibration of the entire vehicle often occurs in the lower speed range of the vehicle, in particular during idling. This vibration is often referred to as "shaking" and has a frequency in the range between 1 and 5 Hz.
The reason for this shaking is the range of tolerances required for mass production of fuel injection equipment. In this case, dimensional variations which can occur within the permitted tolerance ranges for the injection components give rise to fuel injection quantities which differ from cylinder to cylinder. These fuel quantity differences lead to rapid changes in torque which produce vibrations in the engine and body structure. Shaking is therefore an unavoidable consequence of manufacturing tolerances.
These low frequency vibrations can be damped, for example, by adjusting the fuel quantities injected into the individual cylinders. One arrangement for damping shaking comprises, for example, a controller which varies a predetermined desired fuel quantity value as a function of the rapid variations in torque in an attempt to make the torque variations as insignificant as possible.
U.S. Pat. No. 4,688,535 discloses an arrangement in which each cylinder has a control which forms a regulating fuel quantity value for that cylinder as a function of the actual fuel quantity value supplied to that cylinder and of an average of the fuel quantity value for all of the cylinders. Furthermore, in that arrangement the average value is formed from the preceding actual fuel quantity values of all of the cylinders. A disadvantage of that arrangement is the requirement for a complicated individual cylinder correction control which makes the arrangement complex and expensive.
German Patent No. 37 05 586 discloses an arrangement that generates fuel quantity signals which are dependent on the engine operating characteristics, determines from an engine speed signal a smooth running signal, derives from the smooth running signal a fuel quantity error per engine working stroke and cylinder, and superposes a corresponding correcting signal on the fuel quantity signal. The time period of the correcting signal corresponds to one camshaft revolution and the phase relationship of the corrective signal is oriented to the cylinder having the greatest fuel quantity deviation above the average value. In this case, therefore, the fuel quantity correction takes place uniformly for all cylinders.
German Offenlegungsschrift No. 43 19 677 discloses a method for regulating the smooth operation of an internal combustion engine in which a segmented wheel generates segment pulses, with two segment pulses defining each segment, and each cylinder of the internal combustion engine is assigned an actual smooth operating fuel quantity value, a desired smooth operating fuel quantity value, a control deviation, and a controller. Each controller predetermines a cylinder-specific regulating fuel quantity value, starting from the associated control deviation, and the actual smooth operating fuel quantity value and desired smooth operating fuel quantity value are predetermined, starting from at least one segment period duration, the actual smooth operation values and/or the control deviations supplied to the controllers being predetermined by using a weighted average value.
One disadvantage of the conventional methods is that they readjust the fuel quantity for each cylinder on the basis of individual deviations with the result that the overall behavior of the internal combustion engine is uneven. This is particularly true in the case of singular deviations or periodically occurring fluctuations of individual combustions resulting from deposits on the injection valves.